Adaptive suspension systems operate to alter the characteristics of a vehicle suspension system in response to varying road inputs such as vehicle body acceleration and wheel travel. In general, adaptive suspension systems utilize a pressurized fluid which is provided to suspension units, one at each vehicle wheel, to dissipate and/or counteract undesirable external forces. Typically such systems operate under the control of an electronic controller which senses the varying inputs and alters the suspension characteristics by directing fluid flow in an attempt to improve vehicle handling and ride comfort for the road surface over which the vehicle is traveling.
Active suspension systems improve vehicle ride by lowering the natural frequency of the vehicle body and increasing body damping. Several practical problems arise though in developing .adequate responses to road inputs. First, the vehicle parameters are not easily determined and may change from vehicle to vehicle, over time, or with road conditions. Second, minimizing body acceleration must be traded off with wheel travel and controller power. Last, even if vehicle parameters remain constant, suspension calibrations which minimize vertical acceleration change with the shape of the road frequency spectrum. Consequently, it is desirable to have an adaptive controller which can automatically compensate and determine the optimal gains for an active suspension system and- vary the necessary trade-off between body acceleration, wheel travel and controller power.